Abstract: In this study, the phytoplankton of River Oli (Borgu sector) of kainji Lake National Park was investigated at the first time. It recorded total of fifty five taxa, belonging to four major divisions; Bacillariophyta, Chlorophyta, Euglenophyta and Cyanophyta. The taxa were dominated qualitative by green algae and quantitatively by euglenoids in particular Euglena acus. The paucity of phytoplankton composition in the River Oli could be partly due to the poor light penetration into highly turbid water.